FIG. 1 shows a distributed network. The network comprises a number of communication devices 101, 103, 105 and 107. Each device can communicate wirelessly with the other devices that are in effective range of it. In this example the network is a mesh network, meaning that each device relays data for the network. The devices can communicate to propagate data between them. For example, if device 101 transmits a signal, that signal can be received by devices 103 and 107 which are within range of device 101. Devices 103 and 107 can then relay the signal received from device 101 so that it can be received by device 105, which is out of range of device 101 or was not listening when the signal from device 101 arrived. The coverage area of device 101 is illustrated at 108 and the coverage area of device 105 is illustrated at 109. This method of communication allows devices to communicate even though they are out of direct range or not synchronised with each other. Each device may also be connected to, or integrated within, an associated consumer device. So device 101 is connected to a sensor that detects whether window 102 is open or closed, and devices 103 and 105 are connected to light fittings 104 and 106 respectively.
Many mesh networks send data using complex routing tables. The routing tables store routes from one network device to another so that messages can be propagated from source to destination via a series of hops. The topology of the network has to be known in order that routes between the various devices can be determined and stored. An alternative is flood routing. In this method messages do not travel from one device to another via a predefined route. Instead messages are broadcast and any device in range that receives a message retransmits it. A message thus propagates its way through the network, potentially reaching its destination via a number of different routes. Flood routing is very simple to implement and although it may appear inefficient has a number of advantages, particularly for ad hoc networks that may change their topology on a random basis.
Flood routing implies that all devices should theoretically listen continuously for signals from other devices in the network, otherwise there is a risk that data might not reach its destination. Continuous listening increases power consumption. In current mesh networks this is often unimportant because most mesh devices have access to a mains power source, which eliminates the requirement for power saving. It does, however, limit the range of devices that can form part of the network. There is a need to open up mesh networks to a wider range of devices, including those with severe power restrictions.